I wonder why she didn't make efforts to train them when there were long stretches of absolutely nothing to do in the Red Waste (that also would have been a good time to talk to Jorah about her family and/or Westeros in general, but I guess she didn't do that that either). That was the time to get them under control and start training them, when they were still young and small. I agree that she's capable of doing it. But she can only ever ride one of them and she hasn't trained or spent significant time with Viserion or Rhaegal since chaining them in the pit. Now the opportunity to get them under her control looks like ir may have passed. For that reason, I have to give a side-eye to anyone who insists that oh yeah she can conquer Westeros with her dragons. They're just as likely to roast her people as they are the enemy, to say nothing of the people who could end up riding them against her.
I assume that exhaustion and fear of starvation had a big role in that, but there seemed to be plenty of time for training in Vaes Tolorro. I guess that's where she trained them to spew flames? It's just shocking that through all her POVs, in which she spends a great deal of time waiting around for something, we never get one scene of just Dany and the dragons preparing for that conquest she's so keen on getting off the ground. Now that the five year gap won't be happening, this conquest seems like it's going to take place during the dragons' terrible twos, and I agree that might cause some issues that Dany didn't anticipate. I guess we'll just have to wait a decade to find out.